Pressure drop and heat transfer characteristics of flow in channels with periodically grooved parts are investigated for various configurations of the channel, the Reynolds numbers up to 500 and the Prandtl number 7. The flow and temperature fields are assumed to be two-dimensional and fully developed and the wall temperature is kept to be constant. Heat transfer increases significantly after the bifurcation from steady state flow to oscillatory one with the increase of pressure drop penalty. The efficiency defined as the ratio of the heat transfer enhancement to the drag increase is obtained against the Peclet numbers. It is found that the channels with expanded parts show the efficient performance, while the channels with contracted parts are inefficient.